Work out scale reliability instantly with clear inputs, formula shown and shareable results.
The standardised form of Cronbach's alpha is k.rbar/(1 + (k-1)rbar), so reliability rises with both the number of items and their average intercorrelation. Ten items averaging 0.45 give alpha 0.891 - good internal consistency. Only four such items would be needed to reach 0.80, which is why long scales are often unnecessary.
Standardised alpha
alpha = k x rbar / (1 + (k - 1) x rbar)
Items required
k = target(1 - rbar) / (rbar(1 - target))
Above about 0.95 it usually means items are near-duplicates, which wastes respondent time without adding information.
No. Alpha rises with item count regardless of dimensionality, so factor analysis is needed to establish unidimensionality.